We will attempt to establish conditons for accurate transcription of Xenopus ribosomal DNA in vitro. Extracts will be prepared from a line of cultured Xenopus cells and used to transcribe a cloned fragment of ribosomal DNA. This particular plasmid has a unique Xba I restriction site about 800 base paris downstream from the promoter. By cutting at this site we establish an artificial termination signal and can assay for specific initiation by looking for an 800 base long RNA product on a gel. Once conditions are established for specific initiation the extract will be fractionated to identify and study the various components involved.